The present invention relates to a process for making amorphous alloys (either directly or by making master alloy for use in ultimately making amorphous alloy) such as are intended, for example, to at least partially replace crystalline electrical steels in transformers. In particular, this invention relates to a method for making such amorphous alloys which avoids the use of expensive ferroboron.
An amorphous alloy of iron-3% boron-5% silicon, typically containing about 0.5% carbon, has been suggested for a number of magnetic applications, such as in motors and transformers. This alloy has been relatively expensive, however, principally due to the cost of boron. The boron content typically has been added in the form of ferroboron which has been prepared by carbon reduction of a mixture of B.sub.2 O.sub.3, steel scrap, and/or iron oxide (mill scale). That process is highly endothermic and is carried out in submerged electrode arc furnaces. The reduction requires temperatures of about 1600.degree.-1800.degree. C., and the boron recovery is low (typically only about 40% and thus about 2.5 times the final amount of boron must be added) due to the very high vapor pressure of B.sub.2 O.sub.3 at such high reaction temperatures. Furthermore, large amounts of carbon monoxide gas are evolved during the process, necessitating extensive pollution control. Low recovery of boron and the use of extensive pollution control equipment results in a high cost of converting B.sub.2 O.sub.3 (anhydrous boric acid) into ferroboron (ferroboron typically costs more than five times as much as boric acid per pound of contained boron).
Although boric acid can also be reduced by an exothermic aluminothermic process, such a process produces ferroboron with about 4% aluminum (percentages as used herein, are weight percents), which is unsuitable for use in such magnetic applications.